U.S. patent application number 12/438813 was filed with the patent office on 2009-11-12 for pyrogenic titanium dioxide compressed to slugs.
This patent application is currently assigned to EVONIK DEGUSSA GMBH. Invention is credited to Ralph Hofmann, Frank Menzel, Guenter Stein.
Application Number | 20090280309 12/438813 |
Document ID | / |
Family ID | 38669775 |
Filed Date | 2009-11-12 |
United States Patent
Application |
20090280309 |
Kind Code |
A1 |
Hofmann; Ralph ; et
al. |
November 12, 2009 |
PYROGENIC TITANIUM DIOXIDE COMPRESSED TO SLUGS
Abstract
Pyrogenic titanium dioxide is compressed to slugs by
preliminarily deaerating it, compressing it to slugs, and crushing
the slugs and optionally classifying them. The slugs are
characterized by a tamped density (to DIN EN ISO 787-11) of 500 to
1200 g/l.
Inventors: |
Hofmann; Ralph; (Buchen,
DE) ; Stein; Guenter; (Nidderau 4, DE) ;
Menzel; Frank; (Hanau-Steinheim, DE) |
Correspondence
Address: |
OBLON, SPIVAK, MCCLELLAND MAIER & NEUSTADT, L.L.P.
1940 DUKE STREET
ALEXANDRIA
VA
22314
US
|
Assignee: |
EVONIK DEGUSSA GMBH
Essen
DE
|
Family ID: |
38669775 |
Appl. No.: |
12/438813 |
Filed: |
August 9, 2007 |
PCT Filed: |
August 9, 2007 |
PCT NO: |
PCT/EP07/58289 |
371 Date: |
June 8, 2009 |
Current U.S.
Class: |
428/219 |
Current CPC
Class: |
B82Y 30/00 20130101;
C01P 2006/22 20130101; C01P 2004/50 20130101; C09C 1/3646 20130101;
C01P 2006/12 20130101; C01P 2006/11 20130101; C09C 1/3684 20130101;
C01P 2004/52 20130101; C01P 2004/61 20130101; C01P 2004/51
20130101; C01P 2006/82 20130101; C01P 2004/64 20130101 |
Class at
Publication: |
428/219 |
International
Class: |
B32B 9/00 20060101
B32B009/00 |
Foreign Application Data
Date |
Code |
Application Number |
Aug 30, 2006 |
DE |
10 2006 040 591.9 |
Claims
1. Pyrogenic titanium dioxide compressed to slugs, characterized in
that it has a tamped density (to DIN EN ISO 787-11) of 500 to 1200
g/l.
2. Process for preparing pyrogenic titanium dioxide compressed to
slugs according to claim 1, characterized in that pyrogenic
titanium dioxide is optionally preliminarily deaerated and/or
compressed, and compressed to slugs, and the slugs are crushed and
optionally classified.
3. Process for preparing the pyrogenic titanium dioxide compressed
to slugs according to claim 2, characterized in that precompressed
pyrogenic titanium dioxide is used.
4. Use of the pyrogenic titanium dioxide compressed to slugs
according to claim 1 as an additive.
Description
[0001] The invention relates to pyrogenic titanium dioxide
compressed to slugs, to a process for producing the slugs of
pyrogenic titanium dioxide, and to their use.
[0002] It is known that pyrogenic titanium dioxide can be prepared
by means of high temperature or flame hydrolysis from TiCl.sub.4 or
other evaporable titanium compounds (Ullmann's Enzyklopadie der
technischen Chemie, 4th Edition, Volume 21, page 464 (1982).
[0003] Pyrogenic titanium dioxides feature extremely fine
particles, a low bulk density, high specific surface area, very
high purity, spherical particle form and the absence of pores.
[0004] The compression of pyrogenic titanium dioxide is difficult
without binders because pyrogenic titanium dioxide is very dry, and
no capillary forces can bring about the particle binding.
[0005] The pyrogenic titanium dioxide frequently has a high surface
charge which complicates the agglomeration electrostatically.
[0006] For particular applications, it is known that pyrogenic
silicon dioxides can be compressed or shaped to granules.
[0007] It is known that pyrogenic titanium dioxide can be shaped to
titanium dioxide pellets by mixing pyrogenic titanium dioxide with
a moistening agent, a binder, a base and a reshaping assistant, and
extruding this mixture, drying the extrudates and calcining them
(DE 40 12 479 A1).
[0008] It is also known that pyrogenic titanium dioxide can be
shaped to pellets by compressing the pyrogenic titanium dioxide
with urea, graphite and water, drying the mixture, comminuting it,
then extruding or tableting it, and heat-treating the resulting
pellets (EP 0 394 677 A1).
[0009] In addition, pellets of pyrogenic titanium dioxide which can
be used as catalyst supports are described in DE 38 03 894 A1.
[0010] It is also known that pyrogenic titanium dioxide can be
shaped to granules by dispersing the titanium dioxide in water and
spray-drying it. These granules can be used, inter alia, as
catalyst supports (DE 199 28 851 A1).
[0011] The known pellets have the disadvantage that they are not
redispersible or comprise further constituents as well as the
titanium dioxide.
[0012] It is an object of the invention to compress pyrogenic
titanium dioxide so as to obtain a free-flowing product with
defined particle size, good meterability, high bulk density, low
dust content and good redispersibility.
[0013] The invention provides pyrogenic titanium dioxide compressed
to slugs, characterized in that it has a tamped density (to DIN EN
ISO 787-11) of 500 to 1200 g/l.
[0014] In a preferred embodiment of the invention, the tamped
density (to DIN EN ISO 787-11) may be 600 to 800 g/l.
[0015] According to the invention, the slugs of the pyrogenic
titanium dioxide can be classified into various fractions as
follows:
Fraction I: 0.ltoreq.x.ltoreq.500 .mu.m with a tamped density of
678 g/l Fraction II: 200 .mu.m.ltoreq.x.ltoreq.500 .mu.m with a
tamped density of 702 g/l Fraction III: 100
.mu.m.ltoreq.x.ltoreq.200 .mu.m with a tamped density of 606 g/l
Fraction IV: 0.ltoreq.x.ltoreq.100 .mu.m with a tamped density of
605 g/l
[0016] In a preferred form of the invention, the pyrogenic titanium
dioxide compressed to slugs may have a particle size of 200
.mu.m.ltoreq.x.ltoreq.500 .mu.m and a tamped density of 702 g/l
(fraction II).
[0017] This fraction exhibits excellent free-flow properties and a
very low dust content.
[0018] Slugs refer to the more or less elongated intermediate
products which form in the roll compression through the compression
of the starting material. They are optionally comminuted in a
second step.
[0019] The slug properties can be influenced by the procedural
parameters, such as the given process control mode, the compressing
force, the width of the gap between the two rollers and the
pressure hold time which is established through the corresponding
change in the rotational speeds of the compression rollers.
[0020] Compression is understood to mean mechanical compression
without addition of binders. In a particular embodiment of the
invention, the slugs have a defined shape, and the size
distribution can be adjusted by means of screening.
[0021] The inventive pyrogenic titanium dioxide compressed to slugs
has a high transport stability.
[0022] The invention further provides a process for preparing
pyrogenic titanium dioxide compressed to slugs and having a tamped
density (to DIN EN ISO 787-11) of 500 to 1200 g/l, which is
characterized in that pyrogenic titanium dioxide is optionally
preliminarily deaerated and/or compressed, and compressed to slugs,
and the slugs are crushed and optionally classified.
[0023] The process according to the invention is illustrated in
detail with reference to the drawings.
[0024] According to FIG. 1, the pyrogenic titanium dioxide can be
deaerated or precompressed in the preliminary deaerator 1.
[0025] The optionally preliminarily deaerated titanium dioxide is
compressed by means of the compressor 2 to slugs. The resulting
slugs are crushed by means of the apparatus for crushing the slugs
3 and then classified or screened by means of the classifying
apparatus 4.
[0026] According to FIG. 2, which shows the compressor 2
schematically, the titanium dioxide is introduced by means of the
screw 5 into the chamber 6, whence it is entrained by means of the
two rollers 7 and 8 and compressed to slugs.
[0027] When an already precompressed pyrogenic titanium dioxide is
used, it is possible to dispense with this step of preliminary
deaeration. The precompression can be effected, for example, by
means of a vacuum pressure belt filter. The vacuum pressure belt
filter is known from EP 0 280 851 A1.
[0028] The preliminarily deaerated pyrogenic titanium dioxide is
compressed (compacted) to the desired tamped density in the
"compression" step.
[0029] After the compression, the slugs are crushed. If
appropriate, it is subsequently possible to classify or screen
them.
[0030] The fines which are obtained in the screening can be
recycled into the preliminary deaeration step.
[0031] According to the invention, the starting material used in
the preliminary deaeration may be an uncompressed or a
precompressed titanium dioxide.
[0032] The preliminary deaeration can be performed before the
transport or during the transport to the compression.
[0033] Before the transport to the compression, the preliminary
deaeration can be effected by means of a pipe made of a sintered
material, for example sintered metal, to which vacuum is
applied.
[0034] Preliminary deaeration can also be effected in the transport
screw, in which case the transport screw can be connected
downstream of the apparatus which comprises a tube to which vacuum
is applied.
[0035] In a further embodiment of the invention, the transport
screw may be used as the sole apparatus for preliminary
deaeration.
[0036] Moreover, the preliminary deaeration can also be effected by
means of a transport screw which is arranged within a tube to which
vacuum is applied. The tube to which vacuum is applied may consist
of a sintered material, for example sintered metal.
[0037] When the apparatus consists of a preliminary deaeration
tube, for example a tube to which vacuum is applied, and a
transport screw connected downstream, the preliminary deaeration
can be effected in the tube when uncompressed titanium dioxide is
used.
[0038] When precompressed titanium dioxide is used, the preliminary
deaeration can likewise be effected in the tube. It is also
possible to dispense with this preliminary deaeration step.
[0039] When the apparatus which has a transport screw within a tube
to which vacuum is applied is used for preliminary deaeration, both
uncompressed titanium dioxide and precompressed titanium dioxide
can be used.
[0040] The preliminary deaeration of the pyrogenic titanium dioxide
can also be effected by means of filtration on a filter medium, for
example a cloth or sintered material, for example sintered metal,
sintered plastic, sintered ceramic, porous glass, with continuous
filtercake removal by means, for example, of a conveying screw or a
scraper. In one embodiment of the invention, a sintered metal tube
with a metering screw can be used.
[0041] The preliminary deaeration can also be effected by means of
sedimentation.
[0042] The starting material used may be hydrophilic pyrogenic
titanium dioxide or hydrophobic pyrogenic titanium dioxide.
[0043] The hydrophobic pyrogenic titanium dioxide can be prepared
by means of surface modification.
[0044] The surface modification can be effected with one or more
compounds from the following group: [0045] a) organosilanes of the
(RO).sub.3Si(C.sub.nH.sub.2n+1) and (RO).sub.3Si(C.sub.nH.sub.2n-1)
type [0046] R=alkyl, for example methyl, ethyl, n-propyl,
isopropyl, butyl [0047] n=from 1 to 20 [0048] b) organosilanes of
the R'.sub.x(RO).sub.ySi(C.sub.nH.sub.2n+1) and
R'.sub.x(RO).sub.ySi(C.sub.nH.sub.2n-1) type [0049] R=alkyl, for
example methyl, ethyl, n-propyl, isopropyl, butyl [0050] R'=alkyl,
for example methyl, ethyl, n-propyl, isopropyl, butyl [0051]
R'=cycloalkyl [0052] n=from 1 to 20 [0053] x+y=3 [0054] X=1, 2
[0055] y=1, 2 [0056] c) haloorganosilanes of the X.sub.3Si
(C.sub.nH.sub.2n+1) and X.sub.3Si (C.sub.nH.sub.2n-1) type [0057]
X=Cl, Br [0058] n=from 1 to 20 [0059] d) haloorganosilanes of the
X.sub.2(R')Si(C.sub.nH.sub.2n+1) and
X.sub.2(R')Si(C.sub.nH.sub.2n-1) type [0060] X=Cl, Br [0061]
R'=alkyl, for example methyl, ethyl, n-propyl, isopropyl, butyl
[0062] R'=cycloalkyl [0063] n=from 1 to 20 [0064] e)
haloorganosilanes of the X(R').sub.2Si(C.sub.nH.sub.2n+1) and
[0065] X(R').sub.2Si(C.sub.nH.sub.2n-1) type [0066] X=Cl, Br [0067]
R'=alkyl, for example methyl, ethyl, n-propyl, isopropyl, butyl
[0068] R'=cycloalkyl [0069] n=from 1 to 20 [0070] f) organosilanes
of the (RO).sub.3Si(CH.sub.2).sub.n--R' type [0071] R=alkyl, such
as methyl, ethyl, propyl [0072] m=0, from 1 to 20 [0073] R=methyl,
aryl (e.g. --C.sub.6H.sub.5, substituted phenyl radicals) [0074]
--C.sub.4F.sub.9, OCF.sub.2--CHF--CF.sub.3, --C.sub.6F.sub.13,
--O--CF.sub.2--CHF.sub.2 [0075] --NH.sub.2, --N.sub.3, --SCN,
--CH.dbd.CH.sub.2, --NH--CH.sub.2--CH.sub.2--NH.sub.2, [0076]
--N--(CH.sub.2--CH.sub.2--NH.sub.2).sub.2 [0077]
--OOC(CH.sub.3)C.dbd.CH.sub.2 [0078] --OCH.sub.2--CH(O)CH.sub.2
[0079] --NH--CO--N--CO-- (CH.sub.2).sub.5 [0080] --NH--COO
--CH.sub.3, --NH--COO--CH.sub.2--CH.sub.3, --NH--
(CH.sub.2).sub.3Si--(OR).sub.3 [0081]
--S.sub.x--(CH.sub.2).sub.3Si(OR).sub.3, where X=from 1 to 10 and R
may be alkyl, such as methyl, ethyl, propyl, butyl [0082] --SH
[0083] --NR'R''R'''(R'=alkyl, aryl; R''=H, alkyl, aryl; R'''=H,
alkyl, aryl, benzyl, C.sub.2H.sub.4NR''''R''''', where R''''=A,
alkyl and R'''''=H, alkyl) [0084] g) organosilanes of the
(R'').sub.x(RO).sub.nSi(CH.sub.2).sub.m--R' type
[0084] R '' = alkyl = cycloalkyl ##EQU00001## x + y = 1 , 2
##EQU00001.2## x = 1 , 2 ##EQU00001.3## y = 1 , 2 ##EQU00001.4## m
= 0 , from 1 to 20 ##EQU00001.5## [0085] R=methyl, aryl (e.g.
--C.sub.6H.sub.5, substituted phenyl radicals) [0086]
--C.sub.4F.sub.9, --OCF.sub.2--CHF--CF.sub.3, --C.sub.6F.sub.13,
--O--CF.sub.2--CHF.sub.2, [0087] --NH.sub.2, --N.sub.3, --SCN,
--CH.dbd.CH.sub.2, --NH--CH.sub.2--CH.sub.2--NH.sub.2, [0088] --N--
(CH.sub.2--CH.sub.2--NH.sub.2).sub.2, [0089]
--OOC(CH.sub.3)C.dbd.CH.sub.2 [0090] --OCH.sub.2--CH(O)CH.sub.2
[0091] --NH--CO--N--CO-- (CH.sub.2).sub.5 [0092]
--NH--COO--CH.sub.3, --NH--COO--CH.sub.2--CH.sub.3, --NH--
(CH.sub.2).sub.3Si--(OR).sub.3 [0093]
--S.sub.x--(CH.sub.2).sub.3Si(OR).sub.3, where X=from 1 to 10 and
[0094] R may be methyl, ethyl, propyl, butyl SH [0095] --NR'R''R'''
(R'=alkyl, aryl; R''=H, alkyl, aryl; R'''=H, alkyl, aryl, benzyl,
C.sub.2H.sub.4NR'''R''''', where R''''=A, alkyl and R'''''=H,
alkyl) [0096] h) haloorganosilanes of the
X.sub.3Si(CH.sub.2).sub.m--R' type [0097] X=Cl, Br [0098] m=0, from
1 to 20 [0099] R=methyl, aryl (e.g. --C.sub.6H.sub.5, substituted
phenyl radicals) [0100] --C.sub.4F.sub.9,
--OCF.sub.2--CHF--CF.sub.3, --C.sub.6F.sub.13,
--O--CF.sub.2--CHF.sub.2 [0101] --NH.sub.2, --N.sub.3, --SCN,
--CH.dbd.CH.sub.2, [0102] --NH--CH.sub.2--CH.sub.2--NH.sub.2 [0103]
--N-- (CH.sub.2--CH.sub.2--NH.sub.2).sub.2, [0104]
--OOC(CH.sub.3)C.dbd.CH.sub.2 [0105] --OCH.sub.2--CH(O)CH.sub.2
[0106] --NH--CO--N--CO-- (CH.sub.2).sub.5 [0107]
--NH--COO--CH.sub.3, --NH--COO--CH.sub.2--CH.sub.3, --NH--
(CH.sub.2).sub.3Si--(OR).sub.3 [0108]
--S.sub.x--(CH.sub.2).sub.3Si(OR).sub.3, where X=from 1 to 10 and
[0109] R may be methyl, ethyl, propyl, butyl [0110] --SH [0111] i)
haloorganosilanes of the (R)X.sub.2Si(CH.sub.2).sub.n--R' type
[0112] X=Cl, Br [0113] R=alkyl, e.g. methyl, ethyl, propyl [0114]
m=0, from 1 to 20 [0115] R'=methyl, aryl (e.g. --C.sub.6H.sub.5,
substituted phenyl radicals) [0116] --C.sub.4F.sub.9,
--OCF.sub.2--CHF--CF.sub.3, --C.sub.6F.sub.13,
--O--CF.sub.2--CHF.sub.2 [0117] --NH.sub.2, --N.sub.3, --SCN,
--CH.dbd.CH.sub.2, --NH--CH.sub.2--CH.sub.2--NH.sub.2, [0118] --N--
(CH.sub.2--CH.sub.2--NH.sub.2).sub.2 [0119]
--OOC(CH.sub.3)C.dbd.CH.sub.2--OCH.sub.2--CH(O)CH.sub.2 [0120]
--NH--CO--N--CO-- (CH.sub.2).sub.5 [0121] --NH--COO --CH.sub.3,
--NH--COO--CH.sub.2--CH.sub.3,
--NH--(CH.sub.2).sub.3Si--(OR).sub.3, [0122] where R can be methyl,
ethyl, propyl, butyl --S.sub.x--(CH.sub.2).sub.3Si(OR).sub.3, where
R can be methyl, ethyl, propyl, butyl and X can be from 1 to 10
[0123] --SH [0124] j) haloorganosilanes of the
(R).sub.2XSi(CH.sub.2).sub.m--R' type [0125] X=Cl, Br [0126]
R=alkyl, such as methyl, ethyl, propyl, butyl [0127] m=0, from 1 to
20 [0128] R=methyl, aryl (e.g. --C.sub.6H.sub.5, substituted phenyl
radicals) [0129] --C.sub.4F.sub.9, --OCF.sub.2--CHF--CF.sub.3,
--C.sub.6F.sub.13, --O--CF.sub.2--CHF.sub.2 [0130] --NH.sub.2,
--N.sub.3, --SCN, --CH.dbd.CH.sub.2,
--NH--CH.sub.2--CH.sub.2--NH.sub.2, [0131] --N--
(CH.sub.2--CH.sub.2--NH.sub.2).sub.2, [0132]
--OOC(CH.sub.3)C.dbd.CH.sub.2 [0133] --OCH.sub.2--CH(O)CH.sub.2
[0134] --NH--CO--N--CO-- (CH.sub.2).sub.5 [0135]
--NH--COO--CH.sub.3, --NH--COO--CH.sub.2--CH.sub.3, --NH--
(CH.sub.2).sub.3Si--(OR).sub.3. [0136]
--S.sub.x--(CH.sub.2).sub.3Si(OR).sub.3, where X=from 1 to 10 and R
can be methyl, ethyl, propyl, butyl [0137] --SH [0138] k) silazanes
of the
##STR00001##
[0138] type [0139] R=alkyl [0140] R=alkyl, vinyl [0141] 1) cyclic
polysiloxanes of the D 3, D 4, D 5 type, where D 3, D 4 and D 5 are
cyclic polysiloxanes having 3, 4 or 5 units of the
--O--Si(CH.sub.3).sub.2-- type. For example,
octamethylcyclotetrasiloxane=D 4
##STR00002##
[0141] m) polysiloxanes or silicone oils of the type
##STR00003## [0142] m=0, 1, 2, 3, . . . .infin. [0143] n=0, 1, 2,
3, . . . .infin. [0144] u=0, 1, 2, 3, . . . .infin. [0145]
Y.dbd.CH.sub.3, H, C.sub.nH.sub.2n+1 n=1-20 [0146]
Y=Si(CH.sub.3).sub.3, Si(CH.sub.3).sub.2H [0147]
Si(CH.sub.3).sub.2OH, Si(CH.sub.3).sub.2 (OCH.sub.3) [0148]
Si(CH.sub.3).sub.2 (C.sub.nH.sub.2n+1) n=1-20 [0149] R=alkyl, such
as C.sub.nH.sub.2n+1, where n=from 1 to 20, aryl, such as [0150]
phenyl and substituted phenyl radicals, (CH.sub.2).sub.n--NH.sub.2,
H [0151] R'=alkyl, such as C.sub.nH.sub.2n+1, where n=from 1 to 20,
aryl, such as [0152] phenyl and substituted phenyl radicals,
(CH.sub.2).sub.n--NH.sub.2, H [0153] R''=alkyl, such as
C.sub.nH.sub.2n+1, where n=from 1 to 20, aryl, such as [0154]
phenyl and substituted phenyl radicals, (CH.sub.2).sub.n--NH.sub.2,
H [0155] R''=alkyl, such as C.sub.nH.sub.2n+1, where n=from 1 to
20, aryl, such as [0156] phenyl and substituted phenyl radicals,
(CH.sub.2).sub.n--NH.sub.2, H.
[0157] The pyrogenic titanium dioxide can be used directly from the
silo as the starting material in the uncompressed state. In that
case, it may have a tamped density (to DIN EN ISO 787-11) of 40 to
60 g/l.
[0158] Moreover, the pyrogenic titanium dioxide, when it is taken
from containers and used as the starting material, may have a
tamped density (to DIN ISO 787-11) of 50 to 250 g/l.
[0159] Moreover, the pyrogenic titanium dioxide, once compressed,
for example by means of a vacuum pressure belt filter, and used as
the starting material, may have a tamped density (to DIN EN ISO
787-11) of 250 to 450 g/l.
[0160] The pyrogenic titanium dioxide compressed from these
starting materials may have a tamped density of 500 to 1200
g/l.
[0161] When the pyrogenic titanium dioxide is used as the starting
material in hydrophobized form, it may have, in the uncompressed
state, a tamped density (to DIN EN ISO 787-11) of 40 to 250
g/l.
[0162] The hydrophobized pyrogenic titanium dioxide may have, in
the precompressed state, a tamped density of 150 to 450 g/l.
[0163] The precompression can be effected, for example, by means of
a vacuum pressure belt filter. The vacuum pressure belt filter is
known from EP 0 280 851 A1.
[0164] The hydrophobized pyrogenic titanium dioxide can be
compressed by means of a compressor to a tamped density (to DIN EN
ISO 787-11) of 500 to 1200 g/l.
[0165] The pyrogenic titanium dioxide used may have a primary
particle size of 5 to 50 nm and a BET surface area of 30 to 150
m.sup.2/g, preferably 35 to 65 m.sup.2/g.
[0166] The water content of the pyrogenic titanium dioxide used may
be less than 1.5% by weight.
[0167] The pyrogenic titanium dioxide may be precompressed by means
of known processes and apparatus. For example, the apparatus
according to U.S. Pat. No. 4,325,686, U.S. Pat. No. 4,877,595, U.S.
Pat. No. 3,838,785, U.S. Pat. No. 3,742,566, U.S. Pat. No.
3,762,851, U.S. Pat. No. 3,860,682 can be used.
[0168] In a preferred embodiment of the invention, a pyrogenic
titanium dioxide which has been precompressed by means of a
pressure belt filter according to EP 0 280 851 B1 or U.S. Pat. No.
4,877,595 can be used.
[0169] The pyrogenic titanium dioxide can be transported to the
compression, for example, by means of a screw.
[0170] This transport is forced conveying of the pyrogenic titanium
dioxide into the roller gap of the compressing rollers.
[0171] When a conveying screw is used, the pyrogenic titanium
dioxide cannot be precompressed because a preliminary deaeration
takes place here.
[0172] To achieve high bulk densities of the slugs, a conveying
screw and precompressed pyrogenic titanium dioxide can be used.
[0173] The conveying screw used may be a screw with decreasing
volume or with increasing pitch or with decreasing diameter.
[0174] The conveying screw may be surrounded by a tube to which
vacuum is applied. This tube may consist of a sintered material.
The preliminary deaeration of the titanium dioxide is effected here
in the transport screw simultaneously with the transport into the
roller gap.
[0175] The compression to slugs can be effected by means of two
rollers of which one or else both may simultaneously have a
deaeration function.
[0176] It is possible with preference to use two compressing
rollers which may be smooth. They may also be profiled. The profile
may be present either only on one compressing roller or on both
compressing rollers.
[0177] The profile may consist of axially parallel grooves.
Alternatively, it may be composed of recesses (depressions) in any
configuration.
[0178] In a further embodiment of the invention, at least one of
the rollers may be a vacuum roller. In this embodiment, the rollers
may be covered with sintered metal.
[0179] In order to be able to accomplish the deaeration function,
the roller may be produced from sintered metal or be covered with a
filter medium, for example with a cloth.
[0180] If deaeration of the pyrogenic titanium dioxide is possible
by means of the rollers, it is possible to dispense with the
additional preliminary deaeration which can be effected in the
conveying screw or the feed tube.
[0181] When the roller is used for preliminary deaeration, the
roller may have a smooth or profiled surface, and this surface may
be grooved only slightly in order to improve the product
intake.
[0182] The compression should ensure uniform pressing of the
pyrogenic titanium dioxide in order to obtain slugs with a uniform
density.
[0183] To perform the process according to the invention, it is
also possible to use an apparatus as described in document DE-B 1
807 714.
[0184] Preference is given to using smooth rollers in the
compression in order to avoid grit. It is also possible to use one
or two rollers made of sintered material, such as sintered metal or
sintered ceramic, through which deaeration can be effected.
[0185] After the compression, the slugs are crushed. For this
purpose, a screen granulator which defines the particle size by its
mesh size of the screen can be used. The mesh size may be 50 .mu.m
to 20 mm, preferably greater than 200 .mu.m.
[0186] For the crushing of the slugs, it is also possible to use an
apparatus with two contrarotary rollers with a defined gap, or a
toothed roller.
[0187] The crushed slugs can be classified by means of a sifter, of
a screen or of a classifier. This can remove the fines (particles
smaller than 200 .mu.m).
[0188] The sifters used may be crossflow sifters, countercurrent
deflection sifters, etc.
[0189] The classifier used may be a cyclone.
[0190] The fines removed in the classification (particles smaller
than 200 .mu.m) may be recycled into the process according to the
invention.
[0191] After the compression and/or during the fractionation, the
slugs can be sintered in order to increase the solidity.
Determination of the Dust Content
[0192] The dust content is determined to DIN 55992-2.
[0193] A schematic illustration of the apparatus used to determine
the dust content is shown in FIG. 3.
[0194] To determine the dust content, a weighed amount (5 g) of the
inventive slugs or of the comparative product according to DE 199
28 851 A1 is introduced into a charge system at the upper end of
the downpipe. Before the start of the measurement, this is closed
at the bottom by flaps. The end of the downpipe is closed. At the
start of the measurement, this flap is opened for a particular time
interval, so that the sample can fall into the downpipe. During the
falling and when it hits the bottom of the downpipe, the sample
releases dust into the air. The air currents during the falling
ensure uniform distribution of the dust in the tube. Subsequently,
the suspended matter begins to sediment. At the lower end of the
downpipe, the light absorbance which is caused by the suspended
matter is measured by a photometric sensor. The sedimentation is
plotted in the form of the absorbance as a function of time by a
PC. The absorbance is a measure of the relative particle
concentration.
[0195] The integral dust values can be determined from the course
of the absorbance against time. The integral dust values are
determined from the measured sedimentation profile from a start
time ta up to the end of the measurement after 30 s as follows:
I ( ta ) = .intg. to 30 s E ( t ) t where ta = 1 s , 2 s , 4 s , 8
s , 16 s ( 1 ) ##EQU00002##
[0196] These integral dust values describe the amount of dust
released. The integral dust value between 16 s and 30 s is also
known as "dust value". It includes fine dust information and is a
measure of the fine dust content.
[0197] The integral dust value between 1 s and 30 s describes the
total amount of dust which is composed of coarse and fine dust.
[0198] The pyrogenic titanium dioxide compressed in accordance with
the invention to slugs has a lack of dust which is advantageous for
all applications. It can be incorporated into mixtures without loss
and without dust nuisance.
[0199] Even though the pyrogenic titanium dioxide has been
compressed, the inventive slugs have sufficient
redispersibility.
[0200] The pyrogenic titanium dioxide compressed in accordance with
the invention to slugs has no binder.
[0201] The pyrogenic titanium dioxide compressed in accordance with
the invention to slugs can be used without dust as an additive in
cosmetics such as sunscreens, photocatalytic coatings, dyes,
inorganic paint systems or as heat stabilizers in silicone, or as a
raw material for the ceramic industry.
[0202] The pyrogenic titanium dioxide used is P25 titanium dioxide
(AEROXID TiO.sub.2 P25) with the physiochemical characteristics
listed in Table 1. It is known from No. 56 of the "Pigmente"
[Pigments] series of publications "Hochdisperse Metalloxide nach
dem Aerosilverfahren" [High-dispersibility metal oxides by the
Aerosil process], 4th Edition, February 1989, Degussa AG.
TABLE-US-00001 TABLE 1 Titanium dioxide P25 CAS reg. number
13463-67-7 Behaviour towards water Hydrophilic Appearance Loose
white powder BET surface area.sup.1) m.sup.2/g 50 .+-. 15 Mean size
of the primary 21 particles nm Tamped density.sup.2) g/l approx.
100 Specific weight.sup.10) g/ml approx. 3.7 Drying loss.sup.3) on
departure from <1.5 the supplier (at 105.degree. C. for 2 hours)
% Ignition loss.sup.4)7) (2 hours at <2 1000.degree. C.)
pH.sup.5) (in 4% aqueous dispersion) 3-4 SiO.sub.2.sup.8) <0.2
Al.sub.2O.sub.3.sup.8) <0.3 Fe.sub.2O.sub.3.sup.8) <0.01
TiO.sub.2.sup.8) >99.5 ZrO2.sup.8) -- HfO2.sup.8) --
HCl.sup.8)9) <0.3 Screen residue.sup.6) (to Mocker, <0.05 45
.mu.m) % .sup.1)to DIN 66131 .sup.2)to DIN ISO 787/XI, JIS K
5101/18 (not screened) .sup.3)to DIN ISO 787/II, ASTM D 280, JIS K
5101/21 .sup.4)to DIN 55921, ASTM D 1208, JIS K 5101/23 .sup.5)to
DIN ISO 787/IX; ASTM D 1208; JIS K 5101/24 .sup.6)to DIN ISO
787/XVIII; JIS K 5101/20 .sup.7)Based on the substance dried at
105.degree. C. for 2 hours .sup.8)Based on the substance calcined
at 1000.degree. C. for 2 hours .sup.9)HCl content is part of the
glow loss .sup.10)Determined with an air pycnometer
[0203] To prepare the titanium dioxides, a volatile titanium
compound is sprayed into an explosive gas flame composed of
hydrogen and air. In most cases, titanium tetrachloride is used.
This substance hydrolyses under the influence of the water formed
in the hydrogen/oxygen reaction to give titanium dioxide and
hydrochloric acid. The titanium dioxide, after leaving the flame,
enters a so-called coagulation zone in which the titanium dioxide
primary particles and primary aggregates agglomerate. The product
present as a kind of aerosol at this stage is separated from the
gaseous accompanying constituents in cyclones and then aftertreated
with moist hot air.
[0204] The particle sizes of the titanium dioxides can be varied
with the aid of the reaction conditions, for example flame
temperature, hydrogen or oxygen content, amount of titanium
tetrachloride, residence time in the flame or length of the
coagulation zone.
[0205] The BET surface area is determined with nitrogen to DIN 66
131.
[0206] The tamped volume is determined on the basis of ASTM D
4164-88. [0207] Equipment: Engelsmann STA V 2003 tamping volumeter
to DIN 53194, Section 5.2 b-f [0208] Measuring cylinder 250 ml,
marks every 2 ml [0209] Balance with error limit max..+-.0.1 g.
Procedure:
[0210] Set the counter of the tamping volumeter to 1000 strokes.
Tare the measuring cylinder.
[0211] Fill granule into the measuring cylinder up to 250 ml
mark.
[0212] Note the weight (.+-.0.1 g).
[0213] Clamp the measuring cylinder into the tamping volumeter and
switch the instrument on.
[0214] End of tamping.fwdarw.instrument switches off automatically
after 1000 strokes.
[0215] Read the tamped volume accurately to 1 ml.
Calculation:
[0216] E: Granule weight in g [0217] V: Volume read off in ml
[0218] W: Water content in % by weight (determined to test method
P001)
[0218] Tamping density = E .times. ( 100 - W ) V .times. 100
##EQU00003##
[0219] The pH is determined in 4% aqueous dispersion, and in 1:1
water:ethanol in the case of hydrophobic catalyst supports.
[0220] The pulverulent titanium dioxide was compressed with the
Bepex roll compressor. No binders or water were added. The
needle-like compactates were subsequently screen-granulated to a
maximum particle size of 500 micrometers (fraction I). This granule
was subsequently classified by means of screening into fraction II
(200 micrometers.ltoreq.x.ltoreq.500 micrometers) and fractions III
(100 .mu.m.ltoreq.x.ltoreq.200 micrometers) and IV
(0.ltoreq.x.ltoreq.100 micrometers).
[0221] The flow diagram of this process is shown in FIG. 4.
[0222] The conditions established are listed in Table 2.
TABLE-US-00002 TABLE 2 Process parameters of the granulation of the
pyrogenic TiO.sub.2 (AEROXIDE TiO.sub.2 P25) Compressor Type Bepex
L200/50 Roller form Grooved Roller diameter [mm] 200 Roller length
[mm] 50 Product supply into roller Screw gap (120/48) vertical
Compression Roller speed [rpm] 2.9 Peripheral roller speed [m/s]
0.03 Spec. surface pressure [kN/cmRL] 0.6 Speed of the metering
screw [rpm] 95 Capacity [kg/h] 17 Screen granulation Mesh size
[.mu.m] 500 Capacity [kg/h] >17 Screening step 1 (removal of the
fraction with the particle size: 200 .mu.m < x < 500 .mu.m)
Mesh size of the screen [.mu.m] 200 Capacity [kg/h] 24.3 Coarse
material of the [w %] 61 granule bed (200 .mu.m < x < 500
.mu.m) Fine material of the granule [w %] 39 bed (0 < x < 200
.mu.m) Screening step 2 (Classification of the granule bed with a
particle size of: 0 .mu.m < x < 200 .mu.m) Mesh size of the
screen [.mu.m] 100 Coarse material [w %] 50 (100 .mu.m < x <
200 .mu.m) Fine material [w %] 50 (0 < x < 100 .mu.m)
[0223] The sedimentation dust was determined with the Lorenz SP3
measurement apparatus.
[0224] The particle size distribution was determined by means of
HORIBA-LA 920 for fractions III and IV and of AEROPERL P25/20. To
this end, the granules were dispersed in water and then analysed
immediately.
[0225] The particle size distribution of the coarser fraction II
was determined by means of the CAMSIZER from Retsch Technology.
Results:
[0226] The intention was to attempt, with fractions III and IV, to
obtain a granule which has a particle size distribution similar to
the titanium dioxide granule known from DE 199 28 851.
[0227] It was expected that the preparation of the titanium dioxide
compactate by means of the compressing process according to the
invention would be significantly less expensive than by the known
processes by means of spray-drying, because at least the thermal
and hence energy-intensive step of spray-drying would be dispensed
with.
[0228] FIG. 5 shows the particle size distribution of the
spray-dried titanium dioxide granule AEROPERL P25/20 and that of
the TiO.sub.2 granule fraction IV. It can be seen therefrom that
the granule fraction IV has a slightly wider particle size
distribution than AEROPERL P25/20.
[0229] FIG. 6 shows the particle size distribution of granule
fraction II.
[0230] FIG. 7 shows the particle size distribution of granule
fraction III.
[0231] The granule fraction II is characterized by the excellent
flow behaviour and the extreme lack of dust.
[0232] The dusting behaviour and hence the extreme lack of dust of
the granule fraction II with a granule size of 200
.mu.m.ltoreq.x.ltoreq.500 .mu.m can be taken from FIG. 5, in which
the dust is virtually completely sedimented.
[0233] The great decline in the absorbance, which is a measure of
the relative dust concentration, in the range I shows the rapid
sedimentation.
[0234] A low absorbance in the range II after 20 or 30 seconds
shows a low fines content, especially because virtually no
particles remain suspended for a prolonged period.
[0235] It is thus found that not only the coarser granule having a
particle size between 200 and 500 micrometers but also the fine
granule fraction with a similar particle size distribution, such as
AEROPERL TiO.sub.2 P25/20, has a significantly lower dust
content.
[0236] It is possible by the process according to the invention to
increase the tamped density of the pyrogenic titanium dioxide P25
by more than five times.
[0237] The pulverulent pyrogenic TiO.sub.2 P25 has a tamped density
of 130 g/l.
[0238] The spray-dried pyrogenic titanium dioxide AEROPERL P25/20
has a tamped density of 730 g/l.
[0239] Table 3 shows the tamped and bulk densities of the granules
of the pyrogenic titanium dioxide P25 produced in accordance with
the invention.
TABLE-US-00003 TABLE 3 Bulk and tamped density of various granule
fractions and of the starting material AEROXIDE TiO.sub.2 P25
Fraction I Fraction II Fraction III Fraction IV Granule Granule
Granule Granule 0 < x < 500 200 < x < 500 100 < x
< 200 0 < x < 100 .mu.m .mu.m .mu.m .mu.m Bulk 565 602 502
436 density [g/l] Tamped 678 702 606 605 density [g/l]
[0240] FIG. 8 shows the comparison of the dusting behaviour of
inventive slugs with the dusting behaviour of known titanium
dioxide granules according to DE 199 28 851 A1.
[0241] FIG. 9 shows the comparison of the particle size
distribution of the inventive slugs with the particle size
distribution of the known granule P25/20 according to DE 199 28 851
A1 after an ultrasound treatment.
* * * * *